On the origin of TSAR: morphology, diversity and phylogeny of Telonemia

Abstract

Telonemia is a poorly known major phylum of flagellated eukaryotes with a unique combination of morphological traits. Phylogenomics recently revealed the phylogenetic position of telonemids as sister to SAR, one of the largest groups of eukaryotes, comprising Stramenopiles, Alveolata and Rhizaria. Due to this key evolutionary position, investigations of telonemids are of critical importance for elucidating the origin and diversification of an astounding diversity of eukaryotic forms and life strategies. To date, however, only two species have been morphologically characterized from Telonemia, which do not represent this genetically very diverse group. In this study, we established cultures for six new telonemid strains, including the description of five new species and a new genus. We used these cultures to update the phylogeny of Telonemia and provide a detailed morphological and ultrastructural investigation. Our data elucidate the origin of TSAR from flagellates with complex morphology and reconstruction of the ancestral structure of stramenopiles, alveolates and rhizarians, and their main synapomorphic characters. Since telonemids are a common component of aquatic environments, the features of their feeding, behaviour and ecological preferences observed in clonal cultures and the results of global metabarcoding analysis contribute to a deeper understanding of organization of microbial food webs.

Kaonashia insperata gen. et sp. nov., a eukaryotrophic flagellate, represents a novel major lineage of heterotrophic stramenopiles

“…Similar globular and unstructured extrusomes can be found in some rhizarians, Abollifer globosa , for example (Shiratori et al, 2014). The extrusomes we observed are similar in size and overall shape to those found in some telonemids but lack the wheel‐shaped substructure observed in Telonema subtilis (Yabuki et al, 2013) or the nested cylinder conformation observed in Arpakorses (Tikhonenkov, Jamy, et al, 2022). The vesicles located under the cell membrane of Kaonashia are reminiscent of cortical alveoli in alveolates.…”

“…While flagellar hairs in the broad sense are widespread across eukaryotes (Bouck et al, 1978; Kugrens et al, 1987), the long stiff mastigonemes characteristic of stramenopiles (Bouck, 1971) have few close parallels. Nonetheless, similar mastigonemes have been reported in Telonemia (Klaveness et al, 2005; Shalchian‐Tabrizi et al, 2006; Tikhonenkov, Jamy, et al, 2022). These are also present on one flagellum only but in a single row, unlike almost all stramenopile flagellates.…”

A Novel Group of Dynamin-Related Proteins Shared by Eukaryotes and Giant Viruses Is Able to Remodel Mitochondria From Within the Matrix

“…( B ) Phylogenetic distribution of three mitochondrion-targeted DRP types in eukaryotes. The schematic eukaryote phylogenetic tree reflects the most recent phylogenomic studies ( Tice et al 2021 ; Tikhonenkov, Mikhailov, et al 2022 ). Color coding for Opa1, Mgm1, or MidX is provided in the legend on bottom middle.…”

Mitochondrial genomes revisited: why do different lineages retain different genes?

“…Species with available genome and transcriptome assemblies are marked with back circles and triangles, respectively. The cladogram reflecting the phylogenetic relationships among major eukaryotic lineages is based on [ 9 ] and [ 10 ]. The bar charts at the top of the Coulson plots indicate the percentage of investigated taxa where the respective gene is encoded in mitochondrial (purple) and nuclear genome (orange) or lost/not detected.…”